Radioactive substances are both naturally-occurring and found in the environment as a result of activities of man. An example of natural radioactivity is that due to uranium 238, which has been found in drinking water supplies in amounts which may be injurious to man. A good deal of effort is now being expended to clean up radiological contamination of the environment. The first step in dealing with environmental radioisotopes is, of course, to learn where they are located by collecting samples. When samples of water are collected from streams, wells, and surface water accumulations for the purpose of determining whether the water contains radioactive materials, the samples are immediately acidified. It is necessary to add acid (usually hydrochloric acid or, in some cases, nitric acid) in order to keep heavy metals in solution and prevent the metals from binding to the sample container, thus converting all metal ions to cations prior to analysis of the samples in a laboratory. Acidification causes loss of information on the chemical form of the radioactive substance in the environment, that is, whether the substance is in cationic or anionic form. The present invention provides a radiation detector which may be used to determine whether an aqueous sample contains alpha and/or beta radiation emitting substances and, if so, whether they are in cationic or anionic form at the time the sample is collected, that is, before it is acidified and information on oxidation states of the substance is lost. The invention utilizes a sensing element comprised of a single polymer matrix which serves to concentrate radioactive ions, to convert decay particles to photons, and to provide a durable mechanical barrier for the photon measuring device.
It is desirable to check samples in the field to determine if they are sufficiently radioactive that they require special handling. This invention provides semi-quantitative information on radioactive substances. A detector of this invention will be useful in obtaining information for choosing analytical procedures for laboratory analysis of samples.
Drinking water is usually slightly alkaline. Thus, a detector based on cation capture will miss the uranyltricarbonate anion, which is often found in the environment. On the other hand, a commonly used fluorescence-based detector will see only uranium (VI) anions and miss other radioactive ions. This invention may be used to monitor cations and anions simultaneously. A detector may be mounted in a drinking water pipeline for the purpose of providing an alarm signal upon detection of pre-set levels of radiological contaminants in the water. If the water is passed through a bed of ion-exchange material, a detector downstream of the bed may be used to signal when regeneration or replacement of the bed material is necessary. Another mode of using this invention is to lower it down a well to detect radioactivity in ground water.